1. Field of the Invention
The present invention relates to a dense ceramic substrate having good workability and mechanical properties.
2. Description of the Related Arts
A ceramic substrate is used widely, for example, as an insulation substrate for integrated circuits, since it has good insulation property and chemical stability. Recently, a thin film magnetic head which is used in a magnetic disk instrument is produced by forming a circuit on the ceramic substrate.
For example, when the ceramic substrate is used as a substrate of the thin film magnetic head as described in U.S. Pat. No. 4,660,114, its surface must be very smooth to such extent that surface roughness R.sub.max is about 0.02 .mu.m so as to form the magnetic circuit. To this end, a dense ceramic base material which comprises aluminum oxide (Al.sub.2 O.sub.3) and the like as a main component is polished to surface roughness R.sub.max of about 0.02 .mu.m and coated with a ceramic film such as Al.sub.2 O.sub.3 or SiO.sub.2 so as to prepare a substrate, which is used to form a thin film magnetic circuit.
However, even if the surface of the ceramic base material is polished to the surface roughness R.sub.max of not larger than about 0.02 .mu.m, the surface smoothness of the base material has poor reliability and the ceramic film formed on the base material often has poor surface accuracy due to contamination of debris and presence of voids. In addition, the ceramic film cannot be surface finished sufficiently for this use because it cannot be easily machined and tends to suffer from peeling and faults during polishing. Therefore, the ceramic substrate cannot maintain the surface accuracy of the polished ceramic base material and can hardly be used to form the magnetic circuit having desired properties.